A coolant circuit includes a first pipe segment, a second pipe segment, and a seal between the pipe segments which are displaceable relative to each other. A resilient locking tang runs parallel to the first pipe segment and has a detent element. An elongated guide portion runs parallel to and is spaced from the locking tang between the pipe segment and the locking tang. Spaced-apart arms run parallel to the second pipe segment beyond the end of this second pipe segment. An axially parallel web is configured between the arms and is fitted at its end facing the second sub-assembly with a detent shoulder which is engaged from behind by the resilient detent element when the pipe segments are plugged into each other. The resilient tang is received at a closed fit between the arms, and the elongated guide portion is guided by the arms.